Diagnostic Instructions

DTC Descriptors

DTC C0277 03: BMC Primary Piston Position Sensor A and B Circuit Performance Voltage Below Threshold

DTC C129A: BMC Primary Piston Position Sensor A and B Circuit Performance Voltage Below Threshold

DTC C129D: BMC Primary Piston Position Sensor A and B Circuit Performance Voltage Below Threshold

DTC C0277 07: BMC Primary Piston Position Sensor A and B Circuit Voltage Above Threshold

DTC C129B: BMC Primary Piston Position Sensor A and B Circuit Voltage Above Threshold

DTC C129E: BMC Primary Piston Position Sensor A and B Circuit Voltage Above Threshold

DTC C0277 5A: BMC Primary Piston Position Sensor A and B Circuit Plausibility Failure

DTC C12B1: BMC Primary Piston Position Sensor A and B Circuit Plausibility Failure

DTC C12F8: BMC Primary Piston Position Sensor A and B Circuit Plausibility Failure

DTC C120C: BMC Primary Piston Position Sensor A and B Circuit Plausibility Failure

Diagnostic Fault Information

Circuit	Short to Ground	Open/High Resistance	Short to Voltage	Signal Performance
5-Volt Reference	C0277 5A, C12B1, C12F8, C120C, C0161 04, C127D, C0880 00, C12E5, C0880 02, C120F	C0277 03, C129A, C129D, C0277 5A, C12B1, C12F8, C120C, C0161 04, C127D	C0277 5A, C12B1, C12F8, C120C, C0161 04, C127D, C0880 00, C12E5	C0277 5A, C12B1, C12F8, C120C
Brake Master Cylinder Piston Position Sensor Signal Terminal 35	C0277 03, C129A, C129D	C0277 03, C129A, C129D, C0277 5A, C12B1, C12F8, C120C, C0161 04, C127D	C0277 5A, C12B1, C12F8, C120C, C0161 04, C127D, C0880 00, C12E5	C0277 5A, C12B1, C12F8, C120C
Brake Master Cylinder Piston Position Sensor Signal Terminal 9	C0277 03, C129A, C129D	C0277 03, C129A, C129D, C0277 5A, C12B1, C12F8, C120C, C0161 04, C127D	C0277 5A, C12B1, C12F8, C120C, C0161 04, C127D, C0880 00, C12E5	C0277 5A, C12B1, C12F8, C120C
Low Reference	C0294 00, C120C, C12F8, C0161 04, C127D, C0880 00, C12E5, C0455 39	--	--	C0277 5A, C12B1, C12F8, C120C

Circuit/System Description

The electronic brake control module (EBCM) uses input from the brake master cylinder piston position sensor and the brake switch to determine when the brake pedal is being applied and with how much force. These inputs are used to determine the driver's braking intent which is used to the control amount of pressure applied to the wheels.

Conditions for Running the DTC

Conditions for Setting the DTC

C0277 03, C129A, or C129D

The EBCM detects voltage below threshold on signal circuit.

C0277 07, C129B, or C129E

The EBCM detects voltage above threshold on signal circuit.

C0277 5A, C12B1, C12F8, or C120C

This EBCM detects the master cylinder pressure is high when brake master cylinder piston position sensor is reading low travel.

Action Taken When the DTC Sets

Conditions for Clearing the DTC

Reference Information

Schematic Reference

Antilock Brake System Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

ABS Description and Operation

Electrical Information Reference

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

Ignition ON, use a scan tool to observe the EBCM BMC Primary Piston Position Sensor A and B parameter while applying and releasing the brake pedal. The voltage should change between 0 and 5 volts.

Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the brake master cylinder piston position sensor.
2. Ignition OFF, test for less than 5 ohm between the low reference circuit terminal 4 and ground.

⇒	If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the EBCM.

3. Ignition ON, test for 4.8-5.2 volts between the 5-volt reference circuit terminal 2 and ground.

⇒	If less than the specified range, test the 5-volt reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the EBCM.

⇒	If greater than the specified range, test the 5-volt reference circuit for a short to voltage. If the circuit tests normal, replace the EBCM.

4. Verify the scan tool BMC Primary Piston Position Sensor A parameter is less than 1 volt.

⇒	If greater than the specified range, test the signal circuit terminal 1 for a short to voltage. If the circuit tests normal, replace the EBCM.

5. Install a 3A fused jumper wire between the signal circuit terminal 3 and the 5-volt reference circuit terminal 2. Verify the scan tool BMC Primary Piston Position Sensor A parameter is greater than 4.5 volts.

⇒	If less than the specified range, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the EBCM.

6. Verify the scan tool BMC Primary Piston Position Sensor B parameter is less than 1 volt.

⇒	If greater than the specified range, test the signal circuit terminal 3 for a short to voltage. If the circuit tests normal, replace the EBCM.

7. Install a 3A fused jumper wire between the signal circuit terminal 1 and the 5-volt reference circuit terminal 2. Verify the scan tool BMC Primary Piston Position Sensor B parameter is greater than 4.5 volts.

⇒	If less than the specified range, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the EBCM.

8. If all circuits test normal, replace the brake master cylinder piston position sensor.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.